Process of lowering the viscosity of cellulose acetate



Patented Nov. 10, 1931 QUNITED STATES PATENT OFFICE LEONARD-E. BRANCHEN AND GHAU'NCEY U. PRAGHEL DIE ROCHESTER, NEW YORK, AS- SIGNORS TO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORA- 'I'ION, OF NEW YORK PROCESS OF LOWERING THE VISCOSITY OF CELLULOSE ACETATE Ho Drawing. Application filed March 4,

This invention relates to a process for the reduction of the viscosity of cellulose acetate, i. e.', its viscosity when dissolved in a suitable solvent, and particularly to a process whereby cellulose acetate is subjected to viscosity reduction by temperature treatment.

There have been various processes disclosed in the art and in the literature for treating cellulose acetate to reduce its viscosity. Through some molecular rearrangement or other physical or chemical action, resulting from the employment of these processes, the cellulose acetate is rendered less viscous when a given amount is dissolved in a solvent. The particular advantage derived from the use of such a cellulose acetate is primarily that in the preparation of lacquers a su'fiicient amount of the ester can be dissolved inthe solvent mixture so that films of appreciable thicknessmay-be sprayed or brushed upon the surface to be lacquered. Withoutthis viscosity lowering treatment cellulose acetate lacquers are impracticable for most lacquer uses, mainly due to the thinness of the films coated from-them; I In artificial silk manufacture also, the filaments can be extruded moreeconom'ically from low viscosity cellulose acetate, as there is less solvent to recover per hank of silk produced.

- Cellulose acetate has been treated in various manners to effect this desirable result. For example, cellulose acetate has been formed I by high temperature acetylation which, to a certain degree, lowers the viscosity of the cellulose acetate in solution, although a drasticdegradation of the ester often occurs. Gaseous treatment of the cellulose acetate has likewise been suggested for the treatment of the ester in the precipitated or solvated form. J

None of these processes, however, have proven entirely satisfactory due to the film brittleness, limited solubility, or other rea sons, and investigators in this art have, therefore, attempted to provide processes wherein this treatment can be more readily and economically. conducted, without theinherent disadvantages of: the known processes.

An object of the presentinvention is to providea process for so treating cellulose 1930. Serial No. 433,175.

We have found that cellulose acetate pref erably in the finely comminuted form when subjected to an elevated temperature for a certain period will have a considerably lower viscosity, whenitis dissolved. in a solvent, than cellulose 'facetat'egnot sotreated. This pre-treatment of the comminute cellulose acetate through some chemical rearrangement or physical action on the cellulose ester e'fle'cts the viscosity reduction with little dele terious actionupon the ester itself with the result that filmsof goodfiexibility. may be formed therefrom.

In some instances this viscosity reduction takesplace somewhat more favorably in the absence of'solvents of the ester. This is especially'true'in the absence ofany or all sol-I vents which tend to gelatinize the cellulose acetate at room temperature or at the temperature of the reaction. We have found that viscosity reduction can be efficiently and eco nomically carried out by such treatment and particularly so if the ester is'rendered in comminuted form during the removal of the solvent or by other means.

The cellulose acetate can be economically comminutedto the desired extent by spray drying the cellulose acetate in a manner similar to that described in the S. patent to W. B. Webb, 1,516,225, which subdivides the material to particles having the magnitude of approximately 1/200 of an inch or less. This may likewise be effected by the extrusion of the cellulose ester from the solution 1n which it-was acetylated through small orifices into a precipitationsolution such as water or other non-solvent of the ester. "If analka line carbonate or carbonate carrier is added to the aoetylat'ing bath prior to such precipitation as described inthe co-pendmg apph loseaceta'te, prior to itsfiprecipitaition, a low boiling. diquid,=-upon precipitating such a solution into a warm precipitating bath, the cellulose acetate is converted, through the vaporization ofthe low'boiling liquid into'a fiufiy, finely divided form of the ester, very susceptible to our treatment. Any other process :1 for: the-subdivision ofthe. cellulose acetate. either: by a mechanical. '01-. physical:

chemical process may. be employed, .but we have" foundsthatl the above processes have many. advantages.

lose acetate will fsimultaneou-slyremove therefrom a large proportionofthesolventoc'cluded the cellulose acetate. If the spray,

dnying. method -vbe employed, .however, furthere washin-g .ofithecellulose acetate is. use-.

full thecase of theaqueous-.orinonesolvent precipitation \of- .the ester, some subsequentwashingto removetherefrom the solvent. andother contaminating in gradients-.3 resulting the-.esterification is likewise, useful.

Subsequent to the. com-minuti on :or com-.- minution and. idesol-vation oi. L the; cellulose acetate, it is placed. in \asuitahlei containers and hatedeto a temperature 015,120 C. 1to

1&0? CQan-d heldmt that-' temperature pref-. erably while agitating untiLthe-Niscosity of: thescellulose-iacetate hasbeenilowered'to the desired extent. Atatemperature of-120.- 0.. and lower; tl1e. time.-srequired -..to. .obtain the:

maximum. lowering. oft-he viscosity willfoften. be qu te.extens ve,1'unn1ng 1n some-instances.-

to asimuch .as one hundred days. to-obtain themaximumzeflectgwhile athigher==tempera-- tnres, however,rthe-time.of treatmentis much shorter... The: higher! the. :temperature rof treatment,. ,the. more extensive will be the molecular-degradation oflthe cellulose acetate with a corresponding decreasc in thesflexi'mbilityjoiifilm .formed fromsolutionsthereof. It. is. therefore,- desirable to. coordinate the temperature of. the-treatment. with the =fieX-1-i bility of-the final film to such a .poinhtha-t-the: 5 desired viscosity wi-th the optimum afiexibility; willbe realized. e havewfound thatateme perature .in.the neighborhood.of-1509- C. for. most purposes givesasuch optimum results. I

. Inorder that those skilled-imthe-art may, 66 more readily .appreciate. the. advantages-of min-process, ;.We-. are==givingvhere 1 the. results 0t .:two- -'vi-scosity reduction operationse. A- bath-1110f celluloseacetate =1r-ee from solvents and highly :comminuted: was heated. at: a'temr peratune of approximately. 141 Ci. The Nis- Any .oiithe above-describedprocesses for the subdivision-pr comminu-tionofthe cellu cosity of this cellulose acetate in 1: 15 acetone solution was 6.1 seconds prior to treatment. In 7 hours the viscosity was lowered to 2.1 seconds, at 13 hours its viscosity in the same solvent and .in the. same. proportions was 2.0 secondsi. The viscosity ,canbe reduced still lower but the films of cellulose acetate which has been treated for too great a time are not of th'e best quality. A second hatchwastreatedin thesame-mannenand new same temperature, its viscosity was reduced to 1.3 seconds after 7 hours treatment its initial viscosity was-20:7 seconds. At 13 hours the viscosity was reduced to 2.3 seconds and after 29 hours to 0.6secondsl Film fromcellulose acetate solution which has been treated for 29 hours. at this temperature was-notof-the bestquality. but wasneverthelessesuitable. tor-some pu-rposes.--.. The viscosities in .all cases.-.weredetermined in a solution,containing:1 part of cellulose acetateto-5 parts-ofacetone-,by the drop ball method.

From- -the above consideration-s it is apparen-t thatthe viscosity of any type of untreated cellulose acetate, (and when .we refer to the viscosity of cellulose acetate in this disclosure; and in 1 the claims, we of course -imply :the viscosity of cellulose acetate; when. dissolved in a suitable -solvent,) may be reduced byour:

process: The cellulose acetate may contain.-

substantially no SOlVGIItrOI none at all and be treated at anysuitableselevatedztemperature and in any type of:apparatuepreferably in. a

finely com-minuted form, withoutlin any. way departlng. from .thlSJIlVGHtlOh*0IY"S&CI1-fi1Dg' any of: its? a dvant ages.--.

- What we'clainnasour invention -and:desir'e to besecuredbyLetters Patenhof the: United StatesiS-r 1. Process forithe reductionof the viscosity of: cellulose. acetate :which 5 comprises subj ect ing {cellulose acetate: which "is: substantially free-from I volatile solvents to: a temperature of 120 to 180 C.

2::Process :ator the reduction of "the "viscosity of: -cel-lulose acetate r-whic-h" comprises subjecting comminuted' cellulose acetate which-issubstantially free from volatile'soh vent-std a-temperatureof-ELQO to 180 G1 Process for v the reduction of thevviscosity of cellulose acetate: which comprises subjecting comrninuted celluloseacetate which is. substantially iree from wolatile sol vents and 1 having: a particle size of :approxi mately 1/300 of an inch in diameter: or less to'a temperature oiilQOi-to 180-C.

41- Process- .forv thereduction. of the'vis cosity of. :cellulose 1 acetatewhich comprises freeing cellulose I acetate :fromrsolvent media. and then subjecting; it: to a temperature of 120. to 1809 0. I

5. Process fo'rztheredu'ction of theviscosity of cellulose acetate which I comprisesfreein'g cellulose: acetate from all solvents and simultaneously subsdiv idingwit to: a highly. com

minutecl form and subsequently subjecting the solvent-free and comminuted cellulose acetate to a temperature between 1209 and 180 C.

6. Process for the reduction of the viscosity of cellulose acetate which comprises spray drying cellulose acetate and subsequentl heating to a temperature of to 180 until the viscosity of the cellulose acetate has been lowered.

7 Process for the reduction of the Viscosity of cellulose acetate which comprises freeing the cellulose acetate from substantially all solvents, simultaneously sub-dividing to a highly comminuted form and subsequently subjecting the solvent-free and comminuted cellulose acetate to a temperature of approximately C.

Signed at Rochester, New York, this 24th day of February, 1930.

LEONARD E. BRANCHEN. GHAUNCEY U. PRAGHEL.

CERTIFICATE OF CORRECTION.

Patent No. 1,831,795. Granted November 10, 1931, to

LEONARD E. BRANCHEN ET AL.

Signed and sealed this 9th day of February, A. D. 1932.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

